This invention relates to wireless telecommunications networks, and more particularly, to enhancing the compatibility and performance of such networks during soft handoff procedures.
The world-wide proliferation of wireless telecommunications technology presents an opportunity for service providers to profit from an ever-growing demand for convenient, reliable wireless service. As these service providers are well aware, controlling expenses while providing such service poses a significant challenge. Wireless service providers meet this challenge by implementing wireless telecommunications networks comprised of mobile switching centers (MSCs) interconnected to base stations. The MSC completes calls between mobile terminals (that is, any mobile station which uses radio transmission) and other parties. These xe2x80x9cother partiesxe2x80x9d may be other mobile terminals or telephone subscribers served by the public-switched telephone network (PSTN). Each base station is associated with a specific geographic region and serves as an interface between mobile terminals within its region and the MSC.
One consequence of the explosive use of wireless telecommunications and the emergence of numerous wireless service providers in the world market is the implementation of many, diverse wireless networks. The various systems and protocols deployed by these networks often yields equipment incompatibility affecting overall network performance. An especially troubling manifestation of this incompatibility is the inability of existing wireless networks to reconcile incongruent forward link gains (that is, the power supplied by the base station to active mobile terminals) when more than one base station is involved in supporting a call.
Multiple base stations are involved in a call during xe2x80x9csoft handoffxe2x80x9d procedures which routinely occur in code division multiple access (CDMA) wireless telecommunications networks. In a soft handoff situation, each base station handles a certain xe2x80x9clegxe2x80x9d of the call. Although multiple base stations serve various legs of the call, there is generally one base station (i.e., the dominant base station) which maintains a more powerful forward link with the mobile terminal than any other base station. Since disparity among the legs of a call is undesirable, unequal forward link power levels may lead to an attempt, on the part of the nondominant base stations, to increase forward link gains in order to compensate for insufficient gain from a dominant base station. Even if the nondominant base stations are successful in increasing forward link gains to match that of the dominant base station, the increase may not significantly enhance the transmission quality of the call. Indeed, unilateral increases in forward link gains by nondominant base stations adversely affect other active mobile terminals being served by those base stations. In other words, increasing forward link power levels by base stations which are not providing the strongest signal to an active mobile terminal in order to match forward link power levels of dominant base stations causes detriment to other calls served by those base stations and provides marginal benefits to the call in question.
Therefore, there is a need in the art for reconciling forward link power levels among base stations in a wireless telecommunications network.
This need is addressed and a technological advance is achieved by establishing communication between a centralized power control system, a selection/distribution unit (SDU) and participating base stations so that the SDU is notified of the applied forward link power gain setting and overload status. More particularly, when an overload status is attained by a base station, it informs the SDU of the actual value of the power gain level applied and its power overload status. Once the overload status is detected, no further gain increases by the SDU are allowed until the power overload condition is retracted. Gain decreases, however, are allowed. That is, the subsequent gain values can be less than or equal to the value returned with the most recent response indicating overload.
In the preferred embodiment, a MSC includes a SDU equipped with a central power control system. Multiple base stations participating in a soft handoff provide the SDU with actual forward link power gain settings and, if applicable, overload status. This information is transmitted over an SDU/base station communication protocol described in the patent application of Michael F. Dolan, Thomas L. McRoberts, Eshwar Pittampalli and Thomas T. Towle entitled xe2x80x9cWireless Telecommnunications System For Improving Performance And Compatibilityxe2x80x9d, Ser. No. 08/881192, and incorporated by reference herein. Applied forward link gain and overload status information is received and stored in the SDU power control system which monitors and determines all forward link power levels associated with other base stations participating in active calls. When an overload status alert message is received, the SDU is prohibited from increasing forward link gains until the power overload condition is retracted. Simultaneously, the SDU requests all soft handoff participating legs to adjust their respective forward link gain settings to match that of the overloaded leg.